Biblio

Performing a fair exchange without a Trusted Third Party (TTP) was considered to be impossible. With multi party computation and practices like Proof-of-Work (PoW), blockchain accomplishes a fair exchange in a trustless network. Data confidentiality is a key challenge that has to be resolved before adopting blockchain for enterprise applications where tokenized assets will be transferred. Protocols like Zcash are already providing the same for financial transactions but lacks flexibility required to apply in most of the potential use cases of blockchain. Most of the real world application work in a way where a transaction is carried out when a particular action is performed. Also, the zero knowledge proof method used in Zcash, ZKSNARK has certain weaknesses restricting its adoption. One of the major drawbacks of ZKSNARK is that it requires an initial trust setup phase which is difficult to achieve in blockchain ecosystem. ZKSTARK, an interactive zero knowledge proof does not require this phase and also provides security against post quantum attacks. We propose a system that uses two indistinguishable hash functions along with ZKSTARK to improve the flexibility of blockchain platforms. The two indistinguishable hash functions are chosen from SHA3-finalists based on their security, performance and inner designs.

We introduce FairSwap – an efficient protocol for fair exchange of digital goods using smart contracts. A fair exchange protocol allows a sender S to sell a digital commodity x for a fixed price p to a receiver R. The protocol is said to be secure if R only pays if he receives the correct x. Our solution guarantees fairness by relying on smart contracts executed over decentralized cryptocurrencies, where the contract takes the role of an external judge that completes the exchange in case of disagreement. While in the past there have been several proposals for building fair exchange protocols over cryptocurrencies, our solution has two distinctive features that makes it particular attractive when users deal with large commodities. These advantages are: (1) minimizing the cost for running the smart contract on the blockchain, and (2) avoiding expensive cryptographic tools such as zero-knowledge proofs. In addition to our new protocols, we provide formal security definitions for smart contract based fair exchange, and prove security of our construction. Finally, we illustrate several applications of our basic protocol and evaluate practicality of our approach via a prototype implementation for fairly selling large files over the cryptocurrency Ethereum. This article is summarized in: the morning paper an interesting/influential/important paper from the world of CS every weekday morning, as selected by Adrian Colyer

This paper1 introduces the notion of attribute-based concurrent signatures. This primitive can be considered as an interesting extension of concurrent signatures in the attribute-based setting. It allows two parties fairly exchange their signatures only if each of them has convinced the opposite party possesses certain attributes satisfying a given signing policy. Due to this new feature, this primitive can find useful applications in online contract signing, electronic transactions and so on. We formalize this notion and present a construction which is secure in the random oracle model under the Strong Diffie-Hellman assumption and the eXternal Diffie-Hellman assumption.

RFID (Radio-Frequency IDentification) is attractive for the strong visibility it provides into logistics operations. In this paper, we explore fair-exchange techniques to encourage honest reporting of item receipt in RFID-tagged supply chains and present a fair ownership transfer system for RFID-tagged supply chains. In our system, a receiver can only access the data and/or functions of the RFID tag by providing the sender with a cryptographic attestation of successful receipt; cheating results in a defunct tag. Conversely, the sender can only obtain the receiver's attestation by providing the secret keys required to access the tag.